On the reduction of supported iron catalysts studied by M�ssbauer spectroscopy

Huang, Yiping; Anderson, John R.

doi:10.1016/0021-9517(75)90240-7

Cited by 64 publications

(8 citation statements)

References 19 publications

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“…The deposition of small iron particles in zeolitic materials is of great interest because of their potential use in catalytic processes that involve C−C bond formation, such as the Fischer−Tropsch process . The classical preparation method, consisting of ion exchange followed by reduction, is hampered by the difficulty to reduce the cationic species to metallic iron . Alternatively, neutral iron complexes, such as Fe(CO) 5 ,, or Fe(C 5 H 5 ) 2 can be placed in the cages of the zeolite by vapor phase insertion and subsequently decomposed.…”

Section: Introductionmentioning

confidence: 99%

Ferrocene and Dicarbonylcyclopentadienylcobalt in Faujasite-Type Zeolites: A Study of Molecular Motion

et al. 1999

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The anisotropic molecular motion of Fe(C5H5)2 and Co(C5H5)(CO)2 molecules in the supercages of faujasite-type zeolites has been examined by NMR and by Mössbauer spectroscopy. Static 2H quad-echo and {H-}13C CP NMR techniques show that below 225 K the Fe(C5H5)2 molecules have no translational freedom, the only motion being rapid rotation of the cyclopentadienyl rings about their 5-fold axes. This is indicated by an axially symmetric powder pattern (δiso = 69.7 ppm, Ω = 75.0 ppm) in the {1H-}13C CP NMR spectrum and a broad Pake-type powder pattern (QCC = 97.3 kHz) in the 2H NMR spectrum. As the temperature is raised the molecules gain translational freedom, and at temperatures above 358 K isotropic molecular motion is identified as the only type of molecular motion. A model is proposed suggesting that the translational, isotropic motion is mainly caused by intracage, SII→SII jumps of the Fe(C5H5)2 molecules. Based on this model activation energies and diffusion coefficients were calculated from the NMR parameters. The molecular motion of intrazeolite Fe(C5H5)2 depends on the Si/Al ratio of the Na-faujasite host as well, being the highest for Na-faujasites with the lowest Si/Al ratio. The higher amount of sodium cations in the supercages probably causes a decrease in the energy barriers for site-to-site hopping. {1H-}13C CP NMR experiments show that Co(C5H5)(CO)2 molecules get firmly fixed in the zeolite at 183 K. This observation enabled the study of the OC−Co−CO bite angle, φ, by use of 13C Hahn-echo NMR experiments on enriched Co(C5H5)(13CO)2. The presence of an inverted axially symmetric powder pattern with span, Ω, of 127 ppm and a second powder pattern with Ω = 287 ppm indicate changes in the bite angle.

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Section: Introductionmentioning

confidence: 99%

Ferrocene and Dicarbonylcyclopentadienylcobalt in Faujasite-Type Zeolites: A Study of Molecular Motion

et al. 1999

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“…The easiest preparation method producing zeoliteencaged metal clusters is to reduce ion-exchanged metal ions in zeolite with hydrogen gas. For iron or cobalt ion-exchanged zeolite, however, the conventional reduction with hydrogen gas has not been successful since the metal ion has a large negative electrochemical potential and a strong bond to the zeolite framework (Huang and Anderson, 1975; Zhang et al, 1989). Many attempts have been made to improve the reduction of iron or cobalt ion-exchanged zeolites.…”

Section: Introductionmentioning

confidence: 99%

Selective Synthesis and Chain Growth of Linear Hydrocarbons in the Fischer-Tropsch Synthesis over Zeolite-Entrapped Cobalt Catalysts

Koh¹,

Chung²,

Kim³

1995

Ind. Eng. Chem. Res.

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“…It has been reported [15][16][17][18][19] that Fe 1-x O can be stabilized in iron supported catalysts below the critical temperature by interaction with the support through the formation of mixed oxides. In a previous work [7], we observed a close Fe-O-Ce interaction in the precursor oxides prepared by coprecipitation, in which depending on the composition-a Fe-Ce solid solution with a hematite-like or ceria-like structure is developed.…”

Section: Discussionmentioning

confidence: 99%

Use of in situ Mossbauer Spectroscopy and X-Ray Diffraction Techniques for the Characterization of Activated Fe-Ce Catalysts Employed in Fischer-Tropsch Synthesis

Pérez‐Alonso¹,

Ojeda²,

Herranz³

et al. 2008

TOMRJ

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Several Fe-Ce catalysts for FT synthesis were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and a physical mixture of pure Fe and Ce oxide precursors. Previously to CO hydrogenation, catalysts were activated in syngas (50 ml/min, H 2 /CO = 2) at 553 K for 1 h at atmospheric pressure. The iron phases developed after activation pretreatment were identified by XRD and in situ Mössbauer spectroscopy with the objective to study the effect of the addition of cerium on the reduction behavior and catalytic properties of Fe systems. A good correlation between iron phases detected by both techniques was found. The results revealed that the cerium oxide in the samples prepared by coprecipitation produces two effects: (i) lower reduction rate leading to the metastable Fe 1-x O species, and (ii), a decrease in the crystallite size of the iron species upon increasing Ce-contents, as inferred from an increase in superparamagnetic species detected by in situ Mössbauer spectroscopy. Since iron carbides are the "real" active phases in FT synthesis, the stabilization of Fe 1-x O phase after activation is suggested to be responsible for the drop in catalytic activity in Fe-Ce catalysts prepared by coprecipitation during FT synthesis.

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On the reduction of supported iron catalysts studied by M�ssbauer spectroscopy

Cited by 64 publications

References 19 publications

Ferrocene and Dicarbonylcyclopentadienylcobalt in Faujasite-Type Zeolites: A Study of Molecular Motion

Ferrocene and Dicarbonylcyclopentadienylcobalt in Faujasite-Type Zeolites: A Study of Molecular Motion

Selective Synthesis and Chain Growth of Linear Hydrocarbons in the Fischer-Tropsch Synthesis over Zeolite-Entrapped Cobalt Catalysts

Use of in situ Mossbauer Spectroscopy and X-Ray Diffraction Techniques for the Characterization of Activated Fe-Ce Catalysts Employed in Fischer-Tropsch Synthesis

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